1. Field of the Invention
The present invention relates to a diagnostic apparatus for an internal combustion engine, and in particular to a diagnostic apparatus for a diagnostic apparatus for an internal combustion engine to detect a deterioration of fuel consumption caused by an abnormality of an engine.
2. Related Art
There have been proposed the following measures: an apparatus for evaluating a fuel efficient operation, comprising a vehicle data detecting portion for detecting vehicle data as to a fuel efficient operation evaluating item of a vehicle internal combustion engine, a recording portion for recording the vehicle data, an evaluating portion for evaluating the recorded vehicle data in view of the fuel efficient operation and setting evaluation scores thereto, and a synthesizing portion for synthesizing the evaluation points so as to obtain synthetic sores, wherein the recording portion, the evaluating portion and the synthesizing portion are respectively composed of a first to an N-th recording portions, evaluating portions and synthesizing portions which correspond to a first to an N-th running conditions, and there is also provided a correction factor providing portion for calculating fuel consumption rates from fuel consumption values in the first to N-th respective running conditions so as to prepare them as correction factors and a correction synthesizing portion for correcting synthetic scores respectively obtained by the first to N-th synthesizing portions with the correction factors so as to obtain final synthetic scores (as disclosed in JP-A-2003-328845); a fuel data displaying apparatus for displaying an information for informing the driver of a fuel consumption state, wherein a total correction value which is obtained by increasing and a decreasing a fuel injection quantity by a correction factor which is set independent from a manipulation of an accelerator or a brake by the driver during a period from an reference time after a start of an engine to the present time, is averaged by a number or injection cycles in the period, and an information to be displayed for the driver is computed from a value which is obtained by adding the thus obtained averaged value to a fuel injection quantity in accordance with an operating condition of the engine before the correction by the factor in order to display an instantaneous fuel consumption to the driver with no misunderstanding (as disclosed in JP-A-2003-302276), and a method for detecting an abnormality of an internal combustion engine with the use of a learning value (as disclosed in JP-A-2002-202003)
The fuel consumption of the internal combustion engine varies normally within a range about 10 to 20%, depending upon several operating conditions, and accordingly, the conventional technology for directly computing a fuel consumption has been hardly able to detect soon an abnormality of the internal combustion engine which causes a deterioration of fuel consumption even though the driver can be informed of a fuel consumption in order to urge the driver to drive a vehicle in a fuel efficient manner.
The learning value with which an abnormally of an engine is diagnosed is inherently adapted to absorb unevenness as to component parts of an internal combustion engine, and accordingly, due to such unevenness of the component parts, the conventional technology has also been hardly able to detect soon a deterioration of fuel consumption.